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Double cyclic variations in orbital period of the eclipsing cataclysmic variable EX Dra

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arXiv 2017年

作者： Han, Zhong-Tao Qian, Sheng-Bang Voloshina, Irina Zhu, Li-Ying P. O. Box 110 Kunming650216 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences P. O. Box 110 Kunming650216 China University of Chinese Academy of Sciences Yuquan Road 19# Sijingshang Block Beijing100049 China Sternberg Astronomical Institute Moscow State University Universitetskij prospect 13 Moscow119992 Russia

EX Dra is a long-period eclipsing dwarf nova with ~ 2 - 3 mag amplitude outbursts. This star has been monitored photometrically from November, 2009 to March, 2016 and 29 new mid-eclipse times were obtained. By using new data together with the published data, the best fit to the O - C curve indicate that the orbital period of EX Dra have an upward parabolic change while undergoing double-cyclic variations with the periods of 21.4 and 3.99 years, respectively. The upward parabolic change reveals a longterm increase at a rate of P = +7.46×10-11ss-1. The evolutionary theory of cataclysmic variables (CVs) predicts that, as a CV evolves, the orbital period should be decreasing rather than increasing. Secular increase can be explained as the mass transfer between the secondary and primary or may be just an observed part of a longer cyclic change. Most plausible explanation for the double-cyclic variations is a pair of light travel-time effect via the presence of two companions. Their masses are determined to be MAsini' A= 29.3(±0.6)MJupand MBsini'B= 50.8(±0.2)MJup. When the two companions are coplanar to the orbital plane of the central eclipsing pair, their masses would match to brown dwarfs. Copyright © 2017, The Authors. All rights reserved.

关键词： Stars

Rapid instrument exchanging system for the Cassegrain focus of the Lijiang 2.4-m Telescope

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Research in Astronomy and Astrophysics 2015年第6期15卷 918-928页

作者： Yu-Feng Fan Jin-Ming Bai Ju-Jia Zhang Chuan-Jun Wang Liang Chang Yu-Xin Xin Rui-Long Zhang Yunnan Observatories Chinese Academy of Sciences University of Chinese Academy of Sciences Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences

As a facility used for astronomical research, the Lijiang 2.4-m telescope of Yunnan Astronomical Observatories, requires the ability to change one auxiliary instrument with another in as short a time as possible. This arises from the need to quickly respond to scientific programs （e.g. transient observation, time domain studies） and changes in observation conditions （e.g. seeing and weather conditions）. In this paper, we describe the design, construction and test of hardware and software in the rapid instrument exchange system （RIES） for the Cassegrain focal station of this telescope, which enables instruments to be quickly changed at night without much loss of observing time. Tests in the laboratory and at the telescope show that the image quality and pointing accuracy of RIES are satisfactory. With RIES, we observed the same Landolt standard stars almost at the same time with the Princeton Instruments VersArray 1300B Camera （PICCD） and the Yunnan Faint Object Spectrograph and Camera （YFOSC）, while both were mounted at the Cassegrain focus. A quasi-simultaneous comparison shows that the image quality of the optical system inside the YFOSC is comparable with that provided by the PICCD.

关键词： telescopes Lijiang 2.4-m Telescope -- instrumentation photometers -- instrumentation spectrographs -- telescopes automation

The MALATANG survey: Dense gas and star formation from high transition HCN and HCO+ maps of NGC 253

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arXiv 2020年

作者： Jiang, Xue-Jian Greve, Thomas R. Gao, Yu Zhang, Zhi-Yu Tan, Qinghua de Grijs, Richard Ho, Luis C. Michalowski, Michal J. Currie, Malcolm J. Wilson, Christine D. Brinks, Elias Ao, Yiping Zhao, Yinghe He, Jinhua Harada, Nanase Yang, Chentao Jiao, Qian Chung, Aeree Lee, Bumhyun Smith, Matthew W.L. Liu, Daizhong Matsushita, Satoki Shi, Yong Imanishi, Masatoshi Rawlings, Mark G. Zhu, Ming Eden, David Davis, Timothy A. Li, Xiaohu Purple Mountain Observatory Key Laboratory for Radio Astronomy Chinese Academy of Sciences 10 Yuanhua Road Nanjing210033 China Department of Physics and Astronomy University College London Gower Street LondonWC1E 6BT United Kingdom Department of Astronomy Xiamen University Xiamen Fujian361005 China European Southern Observatory Karl-Schwarzschild-Str 2 GarchingD-85748 Germany Department of Physics & Astronomy Macquarie University Balaclava Road SydneyNSW2109 Australia Centre for Astronomy Astrophysics and Astrophotonics Macquarie University Balaclava Road SydneyNSW2109 Australia International Space Science Institute-Beijing Nanertiao Zhongguancun Hai Dian District Beijing100190 China Kavli Institute for Astronomy and Astrophysics Peking University Beijing100871 China Department of Astronomy School of Physics Peking University Beijing100871 China Astronomical Observatory Institute Faculty of Physics Adam Mickiewicz University ul. Sloneczna 36 Pozná n60-286 Poland RAL Space Rutherford Appleton Laboratory Harwell Campus Didcot OxfordshireOX11 0QX United Kingdom Department of Physics and Astronomy McMaster University HamiltonONL8S 4M1 Canada Centre for Astrophysics Research University of Hertfordshire College Lane HatfieldAL10 9AB United Kingdom Yunnan Observatories Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming650011 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Chinese Academy of Sciences South America Center for Astronomy National Astronomical Observatories CAS Beijing100101 China Departamento de Astronomía Universidad de Chile Casilla 36-D Santiago Chile Institute of Astronomy and Astrophysics Academia Sinica 11F of Astronomy-Mathematics Building AS/NTU No.1 Sec. 4 Roosevelt Rd Taipei10617 Taiwan European Southern Observatory Alonso de Córdova 3107 Vitacura Casilla Santiago de C

To study the high-transition dense-gas tracers and their relationships to the star formation of the inner ∼ 2 kpc circumnuclear region of NGC 253, we present HCN J = 4 − 3 and HCO+J = 4 − 3 maps obtained with the James Clerk Maxwell Telescope (JCMT). With the spatially resolved data, we compute the concentration indices r90/r50 for the different tracers. HCN and HCO+ 4-3 emission features tend to be centrally concentrated, which is in contrast to the shallower distribution of CO 1-0 and the stellar component. The dense-gas fraction (fdense, traced by the velocity-integrated-intensity ratios of HCN/CO and HCO+/CO) and the ratio R31 (CO 3-2/1-0) decline towards larger galactocentric distances, but increase with higher SFR surface density. The radial variation and the large scatter of fdense and R31 imply distinct physical conditions in different regions of the galactic disc. The relationships of fdense versus Σstellar, and SFEdense versus Σstellar are explored. SFEdense increases with higher Σstellar in this galaxy, which is inconsistent with previous work that used HCN 1-0 data. This implies that existing stellar components might have different effects on the high-J HCN and HCO+ than their low-J emission. We also find that SFEdense seems to be decreasing with higher fdense which is consistent with previous works, and it suggests that the ability of the dense gas to form stars diminishes when the average density of the gas increases. This is expected in a scenario where only the regions with high-density contrast collapse and form stars. Copyright © 2020, The Authors. All rights reserved.

关键词： Stars

A phenomenological model for the light curve of three quiescent low-inclination dwarf novae and one pre-cataclysmic variable

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arXiv 2018年

作者： Dai, Zhibin Szkody, Paula Kennedy, Mark Su, Jie Medagangoda, N. Indika Robinson, Edward L. Garnavich, Peter M. De Silva, L. Malith M. Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Yuquan Road Shijingshan District Beijing100049 China University of Washington SeattleWA98195 United States Jodrell Bank Centre for Astrophysics School of Physics and Astronomy University of Manchester ManchesterM13 9PL United Kingdom Arthur C. Clarke Institute for Modern Technologies Sri Lanka University of Texas at Austin AustinTX United States University of Notre Dame Notre DameIN46556 United States Sabaragamuwa University of Sri Lanka

We used the light curve code XRBinary to model the quiescent K2 light curves of three low-inclination cataclysmic variables (CVs): 1RXS J0632+2536 (J0632+2536), RZ Leo, TW Vir and the pre-CV WD 1144+011. Optimized light curve models were obtained using a nonlinear fitting code NMfit and visualized by Phoebe 2.0. The disk model of J0632+2536 shows that one hotspot at the edge of the disk is enough to describe its light curve, while the other two dwarf nova (DN): RZ Leo and TW Vir require two hotspots. A typical pre-CV model with a weak irradiation effect for WD 1144+011 can explain its single-hump modulation, and the newly observed spectrum confirms its previous classification. The synthetic analyses for the DN clearly indicate that phase zero of the double-hump modulations occurs around the secondary minimum and the primary hump is mainly caused by the hotspot at the edge of the disk. The quiescent disk has a flat temperature distribution with a power index of ∼ 0.11. The disk model of RZ Leo implies a truncated disk, supporting its previously speculated classification as an intermediate polar (IP). Except for the IP model of RZ Leo, which lacks a component related to the inferred accretion curtain, the models of J0632+2536, TW Vir and WD 1144+011 are consistent with results from the Gaia mission. The derived masses and radii of the secondaries of the three DN are consistent with the semiempirical relations for CV donor stars, while their effective temperatures are higher than the predictions. Irradiation of the donor stars is investigated to explain this discrepancy. Copyright © 2018, The Authors. All rights reserved.

关键词： Modulation

Using the Markov Chain Monte Carlo method to study the physical properties GeV-TeV BL Lac objects

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arXiv 2017年

作者： Qin, Longhua Wang, Jiancheng Yang, Chuyuan Yuan, Zunli Kang, Shiju Mao, Jirong Yunnan Observatory Chinese Academy of Sciences KunmingYunnan Province650011 China University of Chinese Academy of Sciences Beijing China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences Kunming China School of Electrical Engineering Liupanshui Normal University LiupanshuiGuizhou553004 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

We fit the spectral energy distributions (SEDs) of 46 GeV - TeV BL Lac objects in the frame of leptonic one-zone synchrotron self-Compton (SSC) model and investigate the physical properties of these objects. We use the Markov Chain Monte Carlo (MCMC) method to obtain the basic parameters, such as magnetic field (B), the break energy of the relativistic electron distribution (γb′) and the electron energy spectral index. Based on the modeling results, we support the following scenarios on GeV-TeV BL Lac objects: (1) Some sources have large Doppler factors, implying other radiation mechanism should be considered. (2) Comparing with FSRQs, GeV-TeV BL Lac objects have weaker magnetic field and larger Doppler factor, which cause the ineffective cooling and shift the SEDs to higher bands. Their jet powers are around 4.0 × 1045 erg · s−1, comparing with radiation power, 5.0 × 1042 erg · s−1, indicating that only a small fraction of jet power is transformed into the emission power. (3) For some BL Lacs with large Doppler factors, their jet components could have two substructures, e.g., the fast core and the slow sheath. For most GeV-TeV BL Lacs, Kelvin-Helmholtz instabilities are suppressed by their higher magnetic fields, leading few micro-variability or intro-day variability in the optical bands. (4) Combined with a sample of FSRQs, an anti-correlation between the peak luminosity Lpk and the peak frequency νpk is obtained, favoring the blazar sequence scenario. In addition, an anti-correlation between the jet power Pjet and the break Lorentz factor γb also supports the blazar sequence. Copyright © 2017, The Authors. All rights reserved.

关键词： Gamma rays

WZ Sge: An eclipsing cataclysmic variable evolving towards the period minimum

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arXiv 2017年

作者： Han, Z.-T. Qian, S.-B. Voloshina, Irina Zhu, L.-Y. P. O. Box 110 Kunming650216 China Key Laboratory of the Structure and Evolution of Celestial Objects Chinese Academy of Sciences P. O. Box 110 Kunming650216 China University of Chinese Academy of Sciences Yuquan Road 19# Sijingshang Block Beijing100049 China Sternberg Astronomical Institute Moscow State University Universitetskij prospect 13 Moscow119992 Russia

We present the photometric results of the eclipsing cataclysmic variable (CV) WZ Sge near the period minimum (Pmin). Eight new mid-eclipse times were determined and the orbital ephemeris was updated. Our result shows that the orbital period of WZ Sge is decreasing at a rate of P = -2.72(±0.23) × 10-13ss-1. This secular decrease, coupled with previous detection of its donor, suggest that WZ Sge is a pre-bounce system. Further analysis indicates that the observed period decrease rate is about 1.53 times higher than pure gravitational radiation (GR) driving. We constructed the evolutionary track of WZ Sge, which predicts that Pminof WZ Sge is ~ 77.98(±0.90) min. If the orbital period decreases at the current rate, WZ Sge will evolve past its Pminafter ~ 25.3 Myr. Based on the period evolution equation we find M2≈ 4.04(±0.10) × 10-11Moyr-1, which is compatible with the current concept of CV evolution at ultrashort orbital periods. Copyright © 2017, The Authors. All rights reserved.

关键词： Stars

Multi-color photometric investigation of the totally eclipsing binary NO Cam

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arXiv 2017年

作者： Xiao, Zhou Shengbang, Qian Bin, Zhang Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 Graduate University of the Chinese Academy of Sciences Yuquan Road 19 Sijingshang Block Beijing100049

Multi-color photometric light curves of NO Cam in V RCand ICbands are obtained and analyzed simultaneously using the Wilson-Devinney (W-D) program. The solutions suggest that NO Cam is an A-subtype overcontact binary with its mass ratio to be q = 0.439 and a contact degree of f = 55.5%. The small temperature difference (ΔT = 44K) between its two components indicates that the system is under thermal contact. The high orbital inclination (i = 84.5°) strengthens our confidence in the parameters determined from the light curves. All available times of minimum light are collected and period variations are analyzed for the first time. The O - C curve reveals that its period is increasing continuously at a rate of dP/dt = +1.46 × 10-9, which can be explained by mass transfer from the less massive component to the more massive one. After the upward parabolic variation is subtracted, the residuals suggest that there may be a cyclic variation with a period of 2.23 years and an amplitude of A3= 0.00153 days, which may due to the light-travel time effect (LTTE) arising from the gravitational influence of a close-in tertiary component. The close-in companion reveals that early dynamic interaction among triple system may have played very important role in the formation of the W UMa type binaries. Copyright © 2017, The Authors. All rights reserved.

关键词： Photometry

TESS Asteroseismic analysis of the known exoplanet shost star HD 222076

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arXiv 2020年

作者： Jiang, Chen Bedding, Timothy R. Stassun, Keivan G. Veras, Dimitri Corsaro, Enrico Buzasi, Derek L. Mikolajczyk, Przemys law Zhang, Qian-sheng Ou, Jian-wen Campante, Tiago L. Rodrigues, Thaíse S. Nsamba, Benard Bossini, Diego Kane, Stephen R. Ong, Jia Mian Joel Yıldız, Mutlu Orhan, Zeynep Çeiik Örtel, Sibel Wu, Tao Zhang, Xinyi Li, Tanda Basu, Sarbani Cunha, Margarida S. Christensen-Dalsgaard, Jørgen Chaplin, William J. School of Physics and Astronomy Sun Yat-Sen University No. 135 Xingang Xi Road Guangzhou510275 China Department of Physics and Astronomy Aarhus University Ny Munkegade 120 Aarhus C8000 Denmark School of Physics University of Sydney NSW2006 Australia Vanderbilt University Department of Physics and Astronomy 6301 Stevenson Center Ln. NashvilleTN37235 United States 6301 Stevenson Center Ln. NashvilleTN37235 United States Centre for Exoplanets and Habitability University of Warwick CoventryCV4 7AL United Kingdom Department of Physics University of Warwick CoventryCV4 7AL United Kingdom INAF — Osservatorio Astrofisico di Catania via S. Sofia 78 Catania95123 Italy Department of Chemistry & Physics Florida Gulf Coast University 10501 FGCU Boulevard S. Fort MyersFL33965 United States Astronomical Institute University of Wroclaw Mikolaja Kopernika 11 Wroclaw51-622 Poland Yunnan Observatories Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China Key Laboratory for the Structure and Evolution of Celestial Objects Chinese Academy of Sciences 396 Yangfangwang Guandu District Kunming650216 China University of Chinese Academy of Sciences Beijing100049 China Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Rua das Estrelas Porto4150-762 Portugal Departamento de Física e Astronomia Faculdade de Ciências da Universidade do Porto Rua do Campo Alegre s/n Porto4169-007 Portugal Osservatorio Astronomico di PadovaINAF Vicolo dellOsservatorio 5 PadovaI-35122 Italy Max-Planck-Institut für Astrophysik Karl-Schwarzschild-Str. 1 GarchingD-85748 Germany Department of Earth and Planetary Sciences University of California RiversideCA92521 United States Department of Astronomy Yale University P.O. Box 208101 New HavenCT06520-8101 United States Department of Astronomy and Space Sci

The Transiting Exoplanet Survey Satellite (TESS) is an all-sky survey mission aiming to search for exoplanets that transit bright stars. The high-quality photometric data of TESS are excellent for the asteroseismic study of solar-like stars. In this work, we present an asteroseismic analysis of the red-giant star HD 222076 hosting a long-period (2.4 yr) giant planet discovered through radial velocities. Solar-like oscillations of HD 222076 are detected around 203 µHz by TESS for the first time. Asteroseismic modeling, using global asteroseismic parameters as input, yields a determination of the stellar mass (M? = 1.12 ± 0.12M), radius (R? = 4.34 ± 0.21 R), and age (7.4 ± 2.7 Gyr), with precisions greatly improved from previous studies. The period spacing of the dipolar mixed modes extracted from the observed power spectrum reveals that the star is on the red-giant branch burning hydrogen in a shell surrounding the core. We find that the planet will not escape the tidal pull of the star and be engulfed into it within about 800 Myr, before the tip of the red-giant branch is reached. Copyright © 2020, The Authors. All rights reserved.

关键词： Extrasolar planets

Rotational splitting and asteroseismic modelling of the Δ scuti star EE camelopardalis

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arXiv 2017年

作者： Chen, Xinghao Li, Yan Yunnan Observatories Chinese Academy of Sciences P.O. Box 110 Kunming650011 China Key Laboratory for Structure and Evolution of Celestial Objects Chinese Academy of Sciences P.O. Box 110 Kunming650011 China University of Chinese Academy of Sciences Beijing100049 China Center for Astronomical Mega-Science Chinese Academy of Sciences 20A Datun Road Chaoyang District Beijing100012 China

According to the rotational splitting law of g modes, the frequency spectra of EE Cam can be disentangled only with oscillation modes of l = 0, 1, and 2. Fifteen sets of rotational splits are found, containing five sets of l = 1 multiplets and ten sets of l = 2 multiplets. The rotational period of EE Cam is deduced to be Prot = 1.84+0.07 -0.05 days. When we do model fittings, we use two nonradial oscillation modes (f11and f32) and the fundamental radial mode f1. The fitting results show that X2 of the best-fitting model is much smaller than those of other theoretical models. The physical parameters of the best-fitting model are M = 2.04 Mo, Z = 0.028, Teff = 6433 K, log L/Lo = 1.416, R = 4.12 Ro, log g = 3.518, and X2 = 0.00035. Furthermore, we find f11and f32are mixed mode, which mainly characterize the features of the helium core. The fundamental radial mode f1mainly restrict the features of the stellar envelope. Finally, the acoustic radius t0 and the period separation 0 are determined to be 5.80 hr and 463.7 s respectively, and the size of the helium core of EE Cam is estimated to be MHe = 0.181Mo and RHe = 0.0796 Ro. Copyright © 2017, The Authors. All rights reserved.

关键词： Cams